1. Field of the Invention
The present invention relates to a structure for preventing water or the like from intruding in a boot for a universal joint, which is used in a propeller shaft or the like.
2. Description of the Related Art
In a conventional vehicle, a propeller shaft transmitting an output of an engine to a rear wheel is separated in an axial direction, and a universal joint connects separated front and rear shafts. Further, a boot is employed for preventing dust, dirt water or the like from intruding into a connected space between an outer element and inner element of the universal joint. The structure is made such that one end portion of the boot is fitted to the inner element and another end portion is fitted to the outer element.
In the conventional art, to avoid an abnormal expansion and compression, and a resultant breakage of the boot which may result from an internal pressure change of the boot caused by a temperature change due to heat generated in the universal joint, or an internal pressure change of the boot caused by sliding of the universal joint, a groove-like internal pressure adjusting communication passage is provided in a fitting portion of the boot to the inner element. The purpose of this is to communicate internal and external portions of the boot (Japanese Patent Application Laid-Open (JP-A) No. 8-28704).
In the conventional art, in the fitting portion of the boot to the inner element, an end surface to which the communication passage is open is widely exposed to the external portion, so that water resulting from the traveling of a vehicle or a high pressure car wash easily intrudes into the inner portion of the boot from the communication passage mentioned above. When the amount of water intruding to the inner portion of the boot is high, the function of the joint may deteriorate due to rust generation in the universal joint or the like.